Comment on Rosvall: “Intrasexual competition among females: evidence for sexual selection?”

Abstract

Listen

Translate article

There is today ample evidence that sexual selection operates on females and not only on males (reviewed in Clutton-Brock 2007, 2009). The extent of this selection and the mechanisms involved are, however, less well understood and offer numerous interesting possibilities for future research. Rosvall (2011) draws our attention to the phenomenon of female mating competition, which is a topic that deserves more attention. She discusses the ways in which competition among females in the context of mating can lead to variation in female fitness. The 4 predictions examined by Rosvall is a constructive way forward when addressing these questions. In short, female intrasexual competition is expected when mating opportunities (resources or mates) are scarce or when high-quality mates (offering direct or indirect benefits) are scarce (also see Petrie 1983a). As evident from Rosvall’s review, there are several things to keep in mind when looking for, or studying, female intrasexual competition. First, females may usually compete over other things than males. In females, competition over high-quality mates should be more important than competition over quantity of mates. This also means that females can be choosy and competitive at the same time (Halliday 1983; Petrie 1983b; Owens et al. 1994). Second, female competition often seems to be more subtle than competition among males. The behavioral repertoire used in female–female competition is often less overt aggressive than in males (e.g., Forsgren et al. 2004). Females may also show indirect mate competition by excluding others from mating, for example, by physiological suppression of subordinates. Both these points make it easier to overlook competition among females, as compared with competition among males. This, however, does not mean that competition is absent in females. On the contrary, as Rosvall points out, intrasexual competition can indeed be important in females not only in sex-role reversed species. An important take-home message is that it is essential to include all kinds of competition overmatings, not just competition over number of mates, when studying sexual selection. Otherwise, we risk to be biased to detect male–male competition. Future research focusing on female mating competition is needed, and Rosvall suggests priorities for this. An interesting point is that there are indications that competition in males and females may follow different rules, for example, that resourceholding potential can be more important in males, whereas resource value can be more important in females. Recent findings on spiders support this idea (Elias et al. 2010). There are apparently many exciting areas for future research, which hopefully will increase our knowledge on both similarities and differences between the sexes in the context of mating competition.